(Note that the headers change slightly depending on whether you want to use base R, as in your example, or something like ggplot2, as in mine. See the docs here for more exposition on this. TL;DR: include output if you want to use ggplot2 et al.)

To display the image, you've got a couple choices:

org-toggle-inline-images will switch inline image display on and off

org-startup-with-inline-images is a variable which can be set in your config files (init.el / .emacs.d / whathaveyou). If non-nil, images will be shown by default on buffer load.

Also useful is org-redisplay-inline-images, for refreshing an image that's changed on disk if org doesn't auto-reload it.

Is there a more complicated version if I want the png in the emacs buffer and I will be exporting to html (C-c C-e h o) and pdf (C-c C-e l o) versions? Neither of those has images in the output at the moment.
– בנימן הגליליApr 3 '16 at 18:30

2

Without seeing your current code, my hunch is you need to add the header arg :exports both to your src block. By default, only code is exported.
– GastoveApr 4 '16 at 3:29